1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and an electronic device including the semiconductor integrated circuit, and particularly relates to a semiconductor integrated circuit including a charge pump and an electronic device including the semiconductor integrated circuit.
2. Description of the Background Art
An electronic device driven by a battery, such as a mobile telephone or a digital camera, includes a charge pump that boosts a voltage from, for example, the battery. The charge pump boosts an input voltage by a prescribed voltage boost factor and outputs the same. As to the voltage boost factor, factors of 1, 1.5 and 2, for example, are achieved (see Japanese Patent Laying-Open No. 2005-80395 (Patent Document 1)).
When a voltage boost factor of 1.5, for example, is set in a charge pump, it is necessary to supply a current 1.5 times as large as an output current to the charge pump. Therefore, it is necessary to cause the charge pump to output a voltage equal to or slightly larger than a voltage value intended to be obtained as an output voltage, to reduce power consumption. It is desirable to achieve voltage boost factors as various as possible.
FIG. 10 is a drawing that shows a configuration of a typical charge pump achieving voltage boost factors of 1, 1.5 and 2. With reference to FIG. 10, this charge pump includes switches SW1-SW9, external terminals T1-T4, an external terminal TOUT, capacitors C1 and C2, and a capacitor COUT. Switches SW1-SW9 are formed inside a semiconductor integrated circuit. Each of the capacitors is placed outside the semiconductor integrated circuit and connected to the switches in the semiconductor integrated circuit via the external terminals.
FIG. 11 is a drawing that shows a configuration of a typical charge pump achieving voltage boost factors of 1, 1.33, 1.5, and 2. With reference to FIG. 11, this charge pump includes switches SW1-SW14, external terminals T1-T6, an external terminal TOUT, capacitors C1-C3, and a capacitor COUT. As in the charge pump shown in FIG. 10, switches SW1-SW14 are formed inside a semiconductor integrated circuit. Each of the capacitors is placed outside the semiconductor integrated circuit and connected to the switches in the semiconductor integrated circuit via the external terminals.
As such, if a typical charge pump is intended to achieve a voltage boost factor of 1.33 as well, for example, in addition to voltage boost factors of 1, 1.5 and 2, a semiconductor integrated circuit is required to further include five switches and two external terminals, resulting in increase in chip area of the semiconductor integrated circuit.